Almost always cups are where you'll find the biggest Cinderella stories in soccer, where the unexpected happens and David can beat Goliath. Each country's cup is unique, some don't like to give minnows too much room, like Italy's Coppa Italia for example. Others allow clubs from the very bottom of the pyramid to participate, such as the FA Cup, or even clubs from overseas territories, like the Coupe de France. In Japan, however, the Emperor's Cup takes it to the next level.
Not only does the Emperor's Cup allow participants from semi-amateur national tiers and fully amateur regional leagues, but also university and high school teams as well. This concept is very foreign to anyone who is not from Japan, it even sounds like it shouldn't be organized this way, but it's part of this cups history and it gives us incredible stories to this day.
First of all it is worth noting that even though since its creation in 1993 the J-League clubs have been dominating, currently the biggest champion of the Emperor's Cup is the Keio University with 8 titles. Numerous other universities have also won the Emperor's Cup in the past and even a high school back in 1927.
Obviously the biggest upsets occurred prior to 1993 and the professional era of Japanese soccer but there are plenty of amazing stories in recent years. The latest Cinderella story was in 2022 when Ventforet Kofu, a J-League 2 side defeated top flight Sanfrecce Hiroshima and lifted the cup. In 2011 there was an all J-League 2 final between FC Tokyo and Kyoto Sanga. In 2003 the Funabashi Municipal High School took the current Japanese champions, Yokohama F. Marinos, to a penalty shootout in the round of 32.
In addition to the lower division clubs, schools, youth academies and local teams, the Emperor's Cup also once allowed clubs from it's colonies in the first half of the previous century. This means it used to have participants from what is today China, Taiwan and South Korea.
All of this is to say that Japan maybe has one of, if not the most, unique, inclusive and unpredictable cups in the world and it deserves a lot more attention then it receives.